Technical Field
The present invention relates to a fiber coupling unit, to a method for coupling optical fibers to optical waveguides that are integrated into a substrate and extend up to an end face of the substrate, as well as to a fiber coupling system consisting of the fiber coupling unit and the substrate with the integrated waveguides.
Optical glass substrates with planar integrated waveguides require a plurality of optical interfaces for incoupling and outcoupling the optical signals. For this purpose, the integrated waveguides frequently have to be coupled to optical fibers, by means of which the optical signals are transported to and from the optical glass substrate. The coupling of the optical fibers requires a very precise adjustment of the fibers relative to the integrated waveguides. On the other hand, it should also be possible to cost-effectively produce this coupling with minimal effort.
Prior Art
In order to couple optical fibers to integrated optical waveguides in optical glass or polymer substrates that may form, e.g., part of electro-optical circuit boards, it is known to install optical sockets on the edge of the substrate or the circuit board. For this purpose, 3D structures in the circuit board are used as mechanical stops for the installation of the sockets. When polymer waveguides are used, milling and lithography processes can be used for producing the structures in the circuit board. In this case, markings on the circuit board and the socket are also used for aligning these components relative to one another by means of a visual adjustment. However, the considerable tolerances in the manufacture of circuit boards have thus far precluded an industrial application of this technology.
Another option for coupling optical fibers to integrated optical waveguides is described in DE 692 19 843 T2. In this case, a fiber coupling unit consisting of a silicon substrate is used, in which trench structures for accommodating optical fibers are produced by means of conventional silicon etching techniques. The silicon substrate features a contact surface for contacting the surface of the substrate with the integrated waveguides. The trench structures extend up to this contact surface, wherein the end faces of the optical fibers inserted into the trench structures form a stopping face for the end face of the substrate with the integrated waveguides. Two openings with a defined geometry are produced in the contact surface of the silicon substrate, wherein connecting elements formed on the substrate with the integrated waveguides engage into said openings when this substrate is coupled to the silicon substrate. The silicon substrate is exactly positioned relative to the substrate with the integrated waveguides in all three directions in space due to the combination of the contact surface, the stopping face and the engagement of the connecting elements into the openings. In this way, an elaborate active adjustment of the two substrates can be eliminated. However, the use of a silicon substrate with structures that are very exactly produced by means of conventional silicon etching technologies (for example, anisotropic etching, wet-chemical etching or ion beam etching) is associated with relatively high costs.